The signal, to be received by a base station apparatus, suffers interference with various signals, causing the deterioration in reception quality. There is known an adaptive array antenna as an art of suppressing the interference and receiving strongly only the signal arriving in a desired direction. In the adaptive array antenna, the weighting coefficient for multiplied on a reception signal (hereinafter, the weighting coefficient is referred to as “weight”) is adjusted to regulate the amplitude and phase for provision to the reception signal, thereby making it possible to receive strongly only the signal arriving in a desired direction.
Meanwhile, the radio receiver requires a path timing detector circuit (hereinafter, referred to as “path search circuit”) to detect a reception timing of a desired signal. By combining this with the adaptive array antenna art, further correct detection of reception timing is made possible. Incidentally, reception timing is got by, for example, detecting the timing of the correlating peak obtained by the mutual correlating operation with a predetermined signal.
There is, as a conventional adaptive array antenna device having a path search circuit, a disclosure in JP-A-2001-345747. FIG. 14 is a block diagram showing a configuration of a direct-spread CDMA schemed receiver having a conventional adaptive array. In the below, explanation is made on the operation by using FIG. 14. The RF signal, received at antenna elements 1411–141N in the number of n shown in FIG. 14, is sent to the respective radio receiving sections 1421–142N of the antenna elements. In the radio receiving sections 1421–142N, respectively these RF signals are frequency-converted into intermediate frequency (IF band) and amplified by not-shown automatic gain amplifiers.
Furthermore, after orthogonal detection into an I/Q-channel base band signal by the not-shown orthogonal detector, a not-shown A/D converter converts into and outputs a digital signal. Beam-forming sections 1441–1444, because of direct-spread CDMA receivers for the base band signal received at the antenna elements 1411–141N, multiply a code correlating value process output of a not-shown desired wave signal by a plurality of orthogonal beam weights orthogonal one to another. By multiplying beam weights in the beam-forming sections 1441–1444 and thereafter combining them, phase correction is made between the output of the antenna elements 1411–141N.
Due to this, the beam-forming sections 1441–1444 can generate respectively one beams and output them to the corresponding delay profile generating sections 1451–1454. On the basis of the beams a-d outputted from the beam-forming sections 1441–1444, the delay profile generating sections 1451–1454 generate a delay profiles and output them to a path detecting section 1460. Incidentally, the delay profiles represents the status of multipath propagation which is a representation of reception level of arriving path on a delay time axis.
The path detecting section 1460 detects an effective path out of the beam-based delay profiles and notifies a finger section of its timing and beam number.
By the above operation, it is made possible to implement communications with a desired communication area segmented into a plurality of beams and to mitigate the interference of a beam communication signal from other users. By detecting a reception timing after reducing the affection by an interfering user, the accuracy can be improved.
However, in the conventional receiver employing the above configuration, in the case that there is an arrival of a mobile terminal (hereinafter, referred to as “desired user”) radio wave to be intentionally caught by the base station in an intermediate direction of the directional beams due to a plurality of orthogonal beam weights, the directional gain deteriorates and the interference components are not fully suppressed. In this manner, there is a problem of causing a direction dependence that reception-timing detection accuracy varies depending upon an arriving direction of a desired user's radio wave.
The present invention has been made in view of such points, and it is an object to provide a path search circuit which reduces the direction dependence of detection accuracy during path reception timing detection of a desired user's radio wave.